Automatic sheet feeding device

ABSTRACT

A sheet feeding device includes a feeding unit for feeding a mounted sheet, a first drive transmission unit for selectively transmitting a drive to the feeding unit, a conveying unit for conveying the sheet fed by the feeding unit, a second drive transmission unit for selectively transmitting a drive to the conveying unit, and a supporting member for integrally supporting the above-described units.

This application is a continuation of application Ser. No. 08/075,835filed Jun. 14, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic sheet feeding device for use inor with an image forming apparatus, such as a copier, a printer, and afacsimile apparatus, that records on a recording medium, such as paper,an OHP (overhead projector) sheet, and an envelope.

2. Description of the Related Art

FIG. 8 illustrates a laser-beam-printer recording apparatus using anelectrophographic recording technique as a conventional apparatus. Toimprove reliability in this type of sheet feeding apparatus, a sheet islinearly conveyed (this type is hereinafter termed a straight type) toperform recording.

In the straight type, however, the space for inlet and exit units for asheet are added to the main body of the apparatus, causing an increasein the space needed for installing the apparatus.

In order to overcome this problem, a U-like configuration as illustratedin FIG. 9 or an S-like configuration as illustrated in FIG. 10, in whicha conveying path for a sheet is inverted to reduce the actual spaceneeded to install the recording apparatus, has been mostly adopted.

A method has also been proposed in which a sheet is conveyed whilegrasping only an end portion of the sheet with a conveying roller and anobliquely-oriented roller and pressing a reference side of the sheetagainst a conveyance reference guide of the main body of an imageforming apparatus in order to prevent oblique movement of the sheet.

An attempt to reduce the size of an apparatus, to provide high picturequality, and to reduce the production cost of the apparatus has beenmade using the above-described method. However, since a recording mediumis conveyed while pressing a reference side thereof, a greater amount ofworn powder of the recording medium is produced than in otherconventional conveying methods.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described problems.

It is an object of the present invention to provide a sheet feedingdevice having a simpler configuration which can further reduce the sizeof the main body of a recording apparatus, provide high picture quality,reduce the production cost of the apparatus, and solve various kinds ofproblems caused, for example, by powder from wearing of the recordingmedium.

In accordance with these objects, there is provided a sheet feedingdevice comprising feeding means for feeding a mounted sheet, first drivetransmission means for selectively transmitting a drive to the feedingmeans, conveying means for conveying the sheet fed by the feeding meansand and a second drive transmission means for selectively transmitting adrive to the conveying means. A supporting means intricately supportsthe feeding means, the conveying means, the first drive transmissionmeans and the second drive transmission means.

In yet another aspect of the present invention there is provided a sheetconveying device comprising a guide for regulating a lateral position ofa sheet by contacting one side-end of the sheet, a conveying means forconveying the sheet while pressing it against the guide as the side-endportion of the sheet is contacting the guide, a drive transmission meansfor selectively transmitting a drive to the conveying means and a coverfor covering the drive transmission means.

In still another aspect of the present invention there is provided asheet conveying device comprising mounting means for mounting sheets,feeding means for feeding a sheet mounted in the mounting means, aseparation pawl for separating a sheet from other mounted sheet in themounting means in cooperation with the feeding means while contactingone side portion of a leading end portion of the sheet mounted in themounting means, a guide for regulating a lateral position of the sheetfed by the feeding means at the side contactng the separation pawl,conveying means for conveying the sheet fed by the feeding means whilepressing the sheet against the guide as the end portion of the sheet iscontacting the separation pawl, drive transmission means for selectivelytransmitting a drive to the conveying means, a cover for covering thedrive transmission means and a supporting means for intricatelysupporting the feeding means, conveying means, drive transmission meansand the cover.

In still another aspect of the invention each of the above sheetconveying embodiments is provided in conjuction with an image formingapparatus.

The foregoing and other objects, advantages and features of the presentinvention will become more apparent from the following description ofthe preferred embodiment taken in conjuction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an image forming apparatusaccording to an embodiment of the present invention;

FIG. 2 is a front view of the sheet conveying unit;

FIG. 3 is a plan view of the sheet conveying unit and sheet tray;

FIG. 4 is a plan view of the sheet conveying unit

FIG. 5 is a cross-sectional view of the sheet conveying unit;

FIG. 6 is a diagram illustrating the positional relationship between asheet-feeding-roller lever and a sheet-feeding-roller cam in the presentembodiment;

FIG. 7 is a diagram illustrating the manner of assembling components inthe main body of an image forming apparatus; and

FIG. 8 is a diagram illustrating the configuration of a conventionalimage forming apparatus;

FIG. 9 is a diagram illustrating the configuration of anotherconventional image forming apparatus; and

FIG. 10 is a diagram illustrating the configuration of still anothercoventional image forming apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a sheet-feeding/conveying unit mounted in anelectrophotographic laser-beam printer (LBP) of a laser-beam scanningexposure/transfer type according to an embodiment of the presentinvention.

In FIG. 1, a drum-type electrophotographic photosensitive member(hereinafter abbreviated as a drum) 1 is disposed within processcartridge 2, and is rotatably driven around a supporting shaft at apredetermined circumferential speed. A photosensitive member having anorganic or inorganic photoconductive layer is provided on thecircumferential surface of a drum-shaped base member of drum 1.

The surface of drum 1 is uniformly charged at a predetermined positiveor negative potential by a primary charger (not shown) within processcartridge 2 while being rotated, and is then subjected to scanningwriting of target image information at exposure portion 3 withlaser-beam scanning exposure L by laser scanner 4. Thus, anelectrostatic latent image corresponding to the target image informationis sequentially formed on the surface of drum 1.

Laser-beam deflecting mirror 5 deflects laser beam L emitted from laserscanner 4 to exposure portion 3 facing drum 1.

Then, the surface of drum 1 having the latent image thereon is developedwith toner by a developing unit (not shown) within process cartridge 2,whereby a toner image is visualized.

Thereafter, the toner image is sequentially transferred onto a sheetindividually fed by sheet-feeding mechanism 7 to a position betweentransfer roller 6 and drum 1.

The toner image is transferred from the surface of drum 1 onto the sheetby charging the sheet to a polarity opposite to that of the chargedpolarity of the toner image. The sheet is charged by tranfer roller 6disposed at the back side of the sheet. The sheet passing through theposition of transfer roller 6 is separated from the surface of drum 1 bybeing subjected to charge removal by separation/charge-removal needle 9maintained at a potential of an opposite polarity to the polarity oftransfer roller 6. The sheet is then guided to fixing unit 10, in whichthe unfixed toner image on the sheet is fixed as a permanent image.

Thereafter, the sheet is conveyed to a pair of sheet-discharging rollers11 as a transfer material having a fixed image, and the sheet isdischarged onto a sheet-discharge tray (not shown).

Untransferred toner particles and the like may remain on the surface ofdrum 1 after the transfer of the toner image and are removed by acleaning unit (not shown) within process cartridge 2, so that the drum 1is repeatedly used for image formation.

Next, the sheet feeding/conveying unit of the present embodiment will bedescribed in detail with reference to FIGS. 2 through 7.

A main motor (not shown) is provided in the main body of the apparatus,and gears are disposed so as to mesh conveying-roller gear 50 andsheet-feeding-roller driving partial gear 51 by a gear train (notshown). The gear meshing sheet-feeding-roller driving partial gear 51 isdisposed so as to mesh sheet-feeding-roller driving partial gear 51 at anon-geared portion thereof. A sheet-feeding-roller solenoid (not shown)is caught by sheet-feeding-roller stopper 50a to stop rotation.Conveying-roller driving gear 66 provides conveying-roller gear 50 witha driving force.

Clutch 52 incorporates a known planetary gear train. By rotating latchpawl 53 around shaft 55 in the direction of arrow "a" by solenoid 54(see FIG. 2), pawl portion 53a is engaged or disengaged with teeth ofthe outer circumference of sun gear 52a to start or stop the rotation ofsun gear 52a, whereby the transmission of the drive to conveying roller56 disposed on the shaft of clutch 52 is controlled.

If powder from the recording paper, and the like adheres to the contactportion between latch pawl 53 and sun gear (rotatable control member)52a, the friction between latch pawl 53 and sun gear 52a increases, andlatch pawl 53 will not disengage from sun gear 52a. If powder from therecording paper and the like adheres to sun gear 52a, latch pawl 53 doesnot engage the corresponding position of sun gear 52a and latch pawl 53will disengage from sun gear 52a.

In order to overcome such problems, clutch cover 64 prevents intrusioninto the mechanism of powder from the recording paper, and the like. Inaddition, a wall (not shown) is provided in main frame 70 in order toprevent intrusion of powder from the recording paper, and the like.Clutch cover 64 is configured integral with bearing unit 64a so as toalso function as the bearing of output shaft 52b of sun gear 52a.Accordingly, clutch cover 64 can be provided close to output shaft 52bto more effectively prevent intrusion of powder from the recordingpaper, and the like.

With reference to FIG. 4, output-shaft bearing 65 holds output shaft 52bat a predetermined position together with clutch cover 64. Lead wiresfrom solenoid 54 are subjected to pressure calking to solenoid terminals57. Sheet-feeding roller 58 individually separates and conveys sheets 8mounted in cassette 20, and is connected to sheet-feeding-roller drivingpartial gear 51 via sheet-feeding-roller shaft 59.

Sheet-feeding-roller lever 60 rotates around the shaft of clutch 52 toprovide sheet-feeding roller 58 with a rotational force in the directionof arrow b (FIG. 5) by providing cam unit 50a formed on sheet-feedingroller 58 with a pressing force cooperating with sheet-feeding-rollerspring 61.

When no sheet is present on intermediate plate 21, sheet-presence sensorarm 62 rotates in the direction of arrow c to detect the absence ofsheets (see FIG. 5). Sheet-presence sensor arm 62 is capable of rockingback and forth in the directions of arrows E, as illustrated in FIG. 6.

The above-described components are disposed on sheet-feeding frame 63.In addition, sheet-presence sensor arm 62 is rotatably disposed on aboss portion of sheet-feeding frame 63. These components as shown inFIG. 7 constitute sheet-feeding unit N.

The rotation of conveying roller 56 provides a conveying force only forthe uppermost sheet of sheets 8 mounted in sheet-feeding cassette 20.Only the uppermost sheet is separated and conveyed by separation pawl 22(see FIG. 7). At that time, a predetermined pressing force is providedbetween sheets 8 and sheet-feeding roller 58 by the cooperation ofintermediate plate 21 and pressing spring 23 (shown in FIG. 1).

The separated sheet 8 is conveyed along guide 20a serving as conveyingguide means from sheet-feeding cassette 20 shown in FIG. 1 to a portionbetween first obliquely-feeding roller 24 and conveying roller 56. Thesheet 8 is conveyed in synchronization with a rotational speed providedby a driving source (not shown) to pass between second obliquely-feedingroller 25 and conveying roller 56 and between third obliquely-feedingroller 26 and conveying roller 56, and reaches a pressing portionbetween drum 1 and transfer roller 6.

First through third obliquely-feeding rollers 24-26 are pressed againstconveying roller 56 by a pressing mechanism (not shown) atobliquely-feeding angles of 0₁ =1°, 0₂ =4° and 0₃ =4°, respectively, andwith pressing forces of 400 g, 400 g and 300 g, respectively, in adirection to press the side-end of sheet 8 against a main-body referenceguide (not shown, but its conceptual position is shown as referencenumeral 27 in FIG. 3).

FIG. 7 illustrates the positional relationship between theabove-described sheet-feeding frame 63 and other components in the mainbody of the image forming apparatus.

In FIG. 7, reference numeral 70 represents a main frame on which allcomponents are assembled. Main motor 71, serving as a driving source forall the components, is mounted on main frame 70. Gears to supply allnon-driving components (conveying roller 56, sheet-feeding roller 58,drum 1, fixing unit 10 and sheet-discharging roller 11) with the drivingforce from main motor 71 are mounted on driving unit 72.

Sheet-feeding frame 63 is assembled on main frame 70 by insertion in theindicated direction. Only by this assembling operation, connection withpredetermined gears on driving unit 72 is effected, electricalconnection with spring contact 74 and solenoid terminals 57 on mainsubstrate 73 which performs electric control of the main body of therecording apparatus is effected, and sheet-presence sensor arm 62 isaccommodated within a slit in optical sheet-presence sensor 75 on mainsubstrate 73. As shown in FIG. 5, when sheets 8 are absent, a flagportion of sheet-presence sensor arm 62 moves in the direction of arrowb and enters sheet-presence sensor 75. When sheets 8 are present onintermediate plate 21, the flag portion of sheet-presence sensor arm 62disengages from sheet-presence sensor 75.

As described above, according to the configuration of the presentembodiment, the components relating to feeding and conveyance of sheetscan be assembled as one unit. It is thereby possible to improvepositional accuracy in the components, and to perform stable conveyanceof sheets. In addition, it becomes possible to reduce the number ofassembling processes, and therefore to provide a less expensive imageforming apparatus.

Moreover, by adopting single-side oblique conveyance in which arecording medium is conveyed while its reference side is pressed,problems caused by a large amount of worn powder from the recordingmedium produced in a conventional conveying method can be prevented.

While the present invention has been described with respect to what ispresently considered to be the preferred embodiment, it is to beunderstood that the invention is not limited to the disclosedembodiment. To the contrary, the present invention is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

What is claimed is:
 1. A sheet feeding device mountable on a main bodyincluding a frame and a contact for transmitting an electrical controlsignal, said sheet feeding device comprising:feeding means for feeding asheet; drive transmission means for selectively transmitting a drive tosaid feeding means; supporting means for supporting said feeding meansand said drive transmission means; and a terminal, supported by saidsupporting means, and electrically contactable to the contact of themain body by mounting said supporting means on the frame of the mainbody, whereby a control signal for controlling said drive transmissionis transmitted from the contact to said terminal.
 2. A device accordingto claim 1, wherein said drive transmission means comprises a clutch. 3.A device according to claim 2, further comprising a pawl for controllingthe rotation of said clutch.
 4. A device according to claim 3, furthercomprising a cover for covering said clutch.
 5. A device according toclaim 4, wherein said cover is disposed between sheet conveying meansand said drive transmission means.
 6. A sheet conveying device,comprising:a guide for regulating a lateral position of a sheet bycontacting one side-end of the sheet; conveying means for conveying thesheet while pressing it against said guide as the side-end portion ofthe sheet is contacting said guide; drive transmission means forselectively transmitting a drive to said conveying means, said drivetransmission means comprising a control rotator having an outercircumference tooth gear and a pawl selectively engageable with saidouter circumference tooth gear of said control rotator, said drivetransmission means controlling transmission of a drive operation byselectively engaging or disengaging the pawl with said outercircumference tooth gear; and a cover for covering said control rotator.7. A device according to claim 6, wherein said conveying means comprisesa conveying roller rotating in contact with the sheet and anobliquely-feeding roller for urging the sheet against said guide incooperation with said conveying roller.
 8. A device according to claim7, wherein said drive transmission means includes a shaft common to saidconveying roller.
 9. A device according to claim 8, wherein said coveris disposed between said conveying roller and said drive transmissionmeans.
 10. A device according to claim 9, wherein said cover integrallyincludes a bearing for supporting said shaft.
 11. A device according toclaim 7, further comprising conveying guide means for guiding the sheetso that it is conveyed while being curved around said conveying roller.12. A device according to claim 6, further comprising supporting meansfor integrally supporting said conveying means, said drive transmissionmeans and said cover.
 13. A sheet conveying device, comprising:mountingmeans for mounting sheets; feeding means for feeding a sheet mounted insaid mounting means; a separation pawl for separating a sheet from othermounted sheets in said mounting means in cooperation with said feedingmeans while contacting one side portion of a leading-end portion of thesheet mounted in said mounting means; a guide for regulating the lateralposition of the sheet fed by said feeding means at the side contactingsaid separation pawl; conveying means for conveying the sheet fed bysaid feeding means while pressing the sheet against said guide as theend portion of the sheet is contacting said separation pawl; drivetransmission means for selectively transmitting a drive to saidconveying means, said drive transmission means comprising a controlrotator having an outer circumference tooth gear and a pawl selectivelyengageable with said outer circumference tooth gear of said controlrotator, said drive transmission means controlling transmission of adrive operation by selectively engaging or disengaging the pawl withsaid outer circumference tooth gear; a cover for covering said controlrotator; and supporting means for integrally supporting said feedingmeans, said conveying means, said drive transmission means and saidcover.
 14. A device according to claim 13, wherein said conveying meanscomprises a first rotating member for conveying the sheet in contacttherewith.
 15. A device according to claim 14, wherein said conveyingmeans further comprises a second rotating member for conveying the sheetin cooperation with said first rotating member, and wherein said secondrotating member is disposed at an inclined state relative to thedirection of conveyance of the sheet.
 16. A device according to claim15, further comprising conveying guide means for guiding the sheetcurved around said first rotating member.
 17. A device according toclaim 13, wherein said feeding means contacts an end portion of thesheet mounted in said mounting means at an end thereof and at the sidecontacting said separation pawl.
 18. A device according to claim 13,wherein said cover is disposed between said coveying means and saiddrive transmission means.
 19. A device according to claim 18, whereinsaid drive transmission means and said conveying means include a commonshaft, and wherein said cover integrally includes a bearing forsupporting said shaft.
 20. An image forming apparatus mountable on amain body including a frame and a contact for transmitting an electricalcontrol signal, said apparatus comprising:feeding means for feeding asheet; drive transmission means for selectively transmitting a drive tosaid feeding means; supporting means for supporting said feeding meansand said drive transmission means; a terminal, supported by saidsupporting means, and electrically contactable to the contact of themain body by mounting said supporting means on the frame of the mainbody, whereby a control signal for controlling said drive transmissionis transmitted from the contact to said terminal; and image formingmeans for forming an image on a sheet fed by said feeding means.
 21. Animage forming apparatus, comprising:a guide for regulating a lateralposition of a sheet by contacting one side-end of the sheet; conveyingmeans for conveying the sheet while pressing it against said guide asthe side-end portion of the sheet is contacting said guide; drivetransmission means for selectively transmitting a drive to saidconveying means, said drive transmission means comprising a controlrotator having an outer circumference tooth gear and a pawl selectivelyengageable with said outer circumference tooth gear of said controlrotator, said drive transmission means controlling transmission of adrive operation by selectively engaging or disengaging the pawl withsaid outer circumference tooth gear; a cover for covering said controlrotator; and image forming means for forming an image on the sheetconveyed by said conveying means.
 22. An image forming apparatus,comprising:mounting means for mounting sheets; feeding means for feedinga sheet mounted in said mounting means; a separation pawl for separatinga sheet from other mounted sheets in said mounting means in cooperationwith said feeding means while contacting one side portion of aleading-end portion of the sheet mounted in said mounting means; a guidefor regulating the lateral position of the sheet fed by said feedingmeans at the side contacting said separation pawl; conveying means forconveying the sheet fed by said feeding means while pressing the sheetagainst said guide as the end portion of the sheet is contacting saidseparation pawl; drive transmission means for selectively transmitting adrive to said conveying means, said drive transmission means comprisinga control rotator having an outer circumference tooth gear and a pawlselectively engageable with said outer circumference tooth gear of saidcontrol rotator, said drive transmission means controlling transmissionof a drive operation by selectively engaging or disengaging the pawlwith said outer circumference tooth gear; a cover for covering saidcontrol rotator; supporting means for integrally supporting said feedingmeans, said conveying means, said drive transmission means and saidcover; and image forming means for forming an image on the sheetconveyed by said conveying means.